Before formulating the main results, we remind the definition of a weak solution
to Eq. (REF ).
Moreover, throughout the article, we use the well-known notation for sets in \(\mathbb {R}^{n}\) ,
for function spaces and their elements etc. (see, for instance,
[1]}, [2]}, [3]}).
We set
\(G(x, {\rm v})=g(x,{\rm v}){\rm v} \ \ \text{for} \ \ x\in \mathbb {R}^{n}, \ {\rm v}\geqslant 0\) 
